1. Field of the Invention
This invention relates to a machine such as a wood working machine wherein a tool is mounted on a spindle which is rotated by a spindle motor to rotate the tool together therewith, and more particularly to a warning apparatus for a machine of the type mentioned for indicating rotation of the spindle.
2. Description of the Prior Art
A conventional machine of the type mentioned commonly includes a power source lamp disposed, for example, on a front face of a working head. The power source lamp is lit when a power source for a motor driver or driving circuit for driving a spindle motor is turned on in order to give a warning that a spindle is rotating. The power source lamp is extinguished when the power source is turned off. The working machine of such construction, however, is not very safe in that the spindle continues its rotation for some time, due to the inertia thereof, after the power source is turned off.
For example, in a wood working router of the type wherein a working operation is performed automatically by numerical control, a spindle and a tool mounted on the spindle rotate at a very high speed, for example, at 20,000 rpm, and even after a motor driving circuit for driving a spindle motor is turned off, even where the wood working router includes a brake for the spindle, the spindle and the tool will not be stopped immediately, but will continue their rotation for several tens of seconds to several minutes due to their own inertia.
In such a wood working router, since wood to be worked is comparatively frequently operated manually on a table and tools are sharp and in most cases have a blade on a circumferential face thereof, even if a tool is rotating at a low speed, it is very dangerous. Particularly in such a wood working router wherein a spindle motor is accommodated in a motor hood with a dust collecting passageway defined there between and a ring-shaped dust collecting brush is provided so as to extend vertically downwardly from a circumferential edge at a lower end of the motor hood so as to collect chips of wood during working as disclosed, for example, in Japanese Utility Model Publication Application No. 60-13605, Japanese Utility Model Publication Application No. 1-33290 and Japanese Utility Model Laid-Open Application No. 1-72303, the tool is hidden by the dust collecting brush and cannot be observed from outside the dust collecting brush. Accordingly, an operator cannot determine by visual observation whether or not rotation of the tool has stopped. However, since the operator's hand can readily be placed the inside of the dust collecting brush, the danger is particularly high.